This invention relates to a rotor for a rotary gear pump utilizing the trochoidal curve.
It has been well known that an inner rotor curve defined by the periphery of the locus of circular arcs centered on the trochoidal curve, and a theoretical curve of an outer rotor, can be obtained when given the dimensions of a diameter of a base circle, a diameter of a rolling circle, an eccentricity, and a diameter of a rotary path.
However, the inner rotor curve according to these dimensions in prior rotors of this type becomes an inner tooth form having a duplicate portion or an edge portion so that when the rotor of such form is used directly in the pump, the bearing stress (Hertz stress) at the duplicate portion or edge portion increases to promote wear or settling thereat, thereby creating the problem in that the pump performance deteriorates so as to cause vibrations or noises. The term "duplicate portion" as used herein means a loop which may be generated in the inner rotor curve depending on the dimensions of the circles and eccentricity selected for forming the inner rotor curve, and the edge of the resulting inner rotor formed thereat.
In the light of the above problem, this invention has been designed. An object thereof is to provide a rotor for a rotary pump free from the generation of a duplicate portion or edge portion.
An inner rotor for the rotary gear pump utilizing the trochoidal curve can be obtained when a given diameter A of a base circle, diameter B of a rolling circle, an eccentricity e, and a given diameter C of a rotary path as shown in FIG. 1, are utilized to obtain an inner rotor curve TC from the periphery of the locus of circular arcs centered on the trochoidal curve T and also a theoretical curve of an outer rotor.
The inner rotor curve of the prior rotors of this type, however, becomes an inner tooth form as shown in FIG. 2A or FIG. 2B-(II) according to the selection of the above dimensions.
The tooth form in 2A infact is not realizable. In a case where the tooth form in FIG. 2B is directly used for the pump, bearing stress (Hertz stress) at the edge portion 2 in the same figure becomes larger to promote wear or settling at the edge portion 2, thereby having created the problem that the pump performance deteriorates, or vibrations or noises increase.
Therefore, the edge portion in FIG. 2B, when produced, has hitherto been corrected as shown in FIG. 3A and its enlarged view in FIG. 3B. Also, the tooth form of duplicate portion 1 has been corrected as shown in FIG. 3C.
Such correction, however, will lead to a cutout of the part of tooth form by an amount .delta., so that the resulting inner rotor curve, even through different to an extent from the original inner rotor curve, is quite similar to the curve where wear or settling has developed in the amount .delta. after use, thus having lowered the performance of the pump.
The invention is intended to overcome the above disadvantages of prior rotary gear pumps. An object of the invention is to provide a rotor for a rotary gear pump, which is free from creation of the duplicate portion or edge portion and need not be corrected.